Magnetic recording media are widely used in various applications, particularly in the computer industry. The conventional recording medium typically includes a plurality of layers formed on a non-magnetic substrate. The substrate is most commonly disk-shaped and includes a bore through its center. In order to utilize as much of the substrate as possible, the inner and outer diameters of the disk-shaped substrate must meet stringent requirements. One material used for the substrate which is becoming increasingly popular is glass.
Glass substrates are typically produced using at least four processes, each of which is typically carried out at a different location and using different machinery. Glass sheets are first produced and used as bulk material. Solid disks are then cut out of the glass sheets. Subsequently, a bore is drilled through each disk. The surfaces of the disks are then polished to meet requirements prior to applying the layers. Each process requires additional manufacturing cost and the overall production of disk-shaped glass substrates is costly.
Bulk glass sheets are widely used and there is a large industry devoted to their production. As a result, there is also much competition between manufacturers driving the cost of sheets of glass down. Accordingly, it is more economical to buy large sheets of glass and cut the substrates out of those sheets than produce glass disks from scratch. Thus, it would be uneconomical to combine the process of producing the glass and shaping the glass in a single step.
Polishing glass disks for use as the substrates of recording media is carried out using very specific methods and tools in order to meet strict requirements necessary for depositing the remaining layers of the media on the substrate. Due to the specific tools required, there is no clear advantage of combining the polishing step with any of the other steps of manufacturing these substrates.
However, the inventors of the present invention have identified that the step of forming the solid glass disks and forming the bores in the glass disks are similar tasks, both involving cutting through the glass sheet to form a desired shape. Thus, the inventors identified that these steps should be combined in order to reduce manufacturing costs.
In addition to the cost disadvantage that is incurred by having the steps of making the solid disks and forming the bores be separate processes. The present method of forming substrates also suffers from variance between each substrate. Both the outer and inner diameters of the substrate may vary from one substrate to the next. Further, the location of the inner diameter with respect to the outer diameter may also vary from one substrate to the next. Accordingly, in order to meet the stringent requirements of recording media, each step of forming the outer diameter and the inner diameter must be carefully carried out for every substrate. Thus, there is also a need for a method that produces disk-shaped glass substrates in batches, so that the precise formation of the inner and outer diameter may be calculated less frequently.
Another challenge presented when forming glass substrates is that an excess of heat is produced when glass is machined. Thus, when the glass is drilled or cut it becomes very hot. Thermal stresses produced within the glass can lead to cracking within the disk rendering it unfit for use as a disk. Thermal stresses can be avoided by drilling the glass slowly allowing heat to dissipate. However, this slows production time, thereby increasing costs. Therefore, there is a need for a process that can produce glass substrates quickly without losing any considerable amount to cracking or damage.